In automobiles and other types of engine-driven vehicles requiring the use of lubricating fluid such as oil, indicator systems for warning the operator of low oil pressure have long been standard vehicle equipment. These indicator systems provide the operator with a warning that system oil pressure has been lost or is abnormally low. Such warnings are frequently indicative of an inoperable oil pump, a substantial leak or, most often, neglected oil additions in a worn engine.
Such systems have used various techniques for visually indicating low oil pressure to the vehicle operator. For example, many present-day engine lubrication systems include an oil pump which circulates oil from a crankcase reservoir through various supply lines to continuously lubricate engine components. The oil is pumped from the reservoir through a conduit having an open end near the bottom of the crankcase. Included in the. system on the transmitting side of the pump is a pressure sensitive device which is electrically connected to a visual indicating means such as a warning light on the vehicle dashboard. The pressure sensitive device can be, for example, a conventional diaphragm assembly which spatially operates a relay or other type of contact switch for selectively illuminating the warning light. If the oil level in the crankcase is too low, and little or no oil is pumped toward the diaphragm, the warning light continues to remain illuminated after the engine is started by the operator.
Unfortunately, the type of conventional warning system described above does not provide any prior warning of loss of oil pressure. That is, the oil pressure loss warning may occur too late to prevent engine damage, or it may occur when the vehicle is far from a place where the defect or malfunction causing the oil pressure loss can be timely and conveniently repaired. Furthermore, such oil pressure loss can also occur merely from neglected servicing of the vehicle by the operator. Again, the warning provided by the aforedescribed system will not occur until a high probability of serious damages exists. With the continuing increase in time periods between servicing of modern engine components such as spark plugs, ignitions, etc., the probability of neglecting periodic oil servicing has also increased. Accordingly, warning systems which include indication only of oil pressure loss are becoming increasingly unacceptable.
Several prior art vehicle warning systems have been developed to provide vehicle operators with indications of actual reservoir oil levels or of low oil levels prior to complete loss of pressure. For example, the Carothers, Jr. U.S. Pat. No. 3,333,259, issued July 25, 1967, discloses an oil level indicator including a conduit disposed in an oil pan which either draws oil or air up through the conduit, depending upon the level of oil in the pan. A vacuum, which is created through a piston-type switch, draws the oil or air into the line which is then communicated to a diaphragm actuator for an indicator light. When the oil level is low, air is drawn through the line due to the vacuum. The air pressure is not sufficient to move the diaphragm, which thus remains in a normally closed position and actuates a warning light.
The Kelly U.S. Pat. No. 2,800,648, issued July 23, 1957, describes an oil level indicator including two tubes which terminate at different heights in the crankcase. The tubes communicate to a casing or head including venturis which create a vacuum or suction for drawing either air or oil into the tubes, dependent upon the level of the tube with respect to oil in the crankcase. A diaphragm valve responds to the pressure differential in the tubes so as to activate a warning light.
In the Raby U.S. Pat. No. 2,588,761, issued Mar. 11, 1952, an oil level indicator includes a tube disposed in an oil pan which is communicative with a diaphragm-operated switch. The operator indicator is operated by communicating the vacuum from the engine to the level-indicating device which draws oil into a chamber in which a float is disposed. As the level in the chamber rises, the float closes a valve which in turn causes movement of the diaphragm to complete an indicating circuit.
Though the aforedescribed patents disclose systems adapted to indicate a low oil level to an operator prior to complete oil pressure loss, the systems either must be completely substituted for industry-standard oil pressure warning systems, or they include a substantial number of components additional to those of industry-standard warning systems. Accordingly, such systems are difficult and expensive, if not impossible, to retrofit into existing vehicles. Furthermore, the systems are more expensive and complex than standard oil pressure warning systems, even if they are only fitted to new vehicles. For example, certain of these prior art systems require visual indicator devices in addition to an oil pressure warning light. Such systems would therefore also require redesign of the vehicle's dashboard instrument arrangement.